Unconventional Weyl semimetals have attracted intensive research interest in condensed-matter physics and materials science, but they are very rare two dimensions. In this work, based on symmetry analysis first-principles electronic structure calculations, we predict that the Si/Bi van der Waals heterostructure is a two-dimensional unconventional quadratic double semimetal with strong spin-orbi...

We report calculations of the electronic structure of silicene and the stability of its weakly buckled honeycomb lattice in an external electric field oriented perpendicular to the monolayer of Si atoms. The electric field produces a tunable band gap in the Dirac-type electronic spectrum, the gap being suppressed by a factor of about eight by the high polarizability of the system. At low electr...

We study with first-principles methods the interplay between bulk and surface Dirac fermions in three dimensional Dirac semimetals. By combining density functional theory with the coherent potential approximation, we reveal a topological phase transition in Na_{3}Bi_{1-x}Sb_{x} and Cd_{3}[As_{1-x}P_{x}]_{2} alloys, where the material goes from a Dirac semimetal to a trivial insulator upon chang...

We present molecular dynamics simulation evidence for a freezing transition from liquid silicon to quasi-twodimensional (quasi-2D) bilayer silicon in a slit nanopore. This new quasi-2D polymorph of silicon exhibits a bilayer hexagonal structure in which the covalent coordination number of every silicon atom is four. Quantum molecular dynamics simulations show that the stand-alone bilayer silico...

We use determinantal quantum Monte Carlo simulations and numerical linked-cluster expansions to study thermodynamic properties and short-range spin correlations of fermions in the honeycomb lattice. We find that, at half filling and finite temperatures, nearest-neighbor spin correlations can be stronger in this lattice than in the square lattice, even in regimes where the ground state in the fo...

Three single-layer tetragonal silicon carbides (SiCs), termed as T1, T2 and T3, are proposed by density functional theory (DFT) computations. Although the three structures have the same topological geometry, they show versatile electronic properties from a semiconductor (T1), a semimetal (T2) to a metal (T3). The versatile properties originate from the rich bonds between Si and C atoms. The nan...

We report the magnetoresistance (MR) and Shubnikov de Haas (SdH) oscillations in the polycrystalline p-type ZrTe5.We observed a small cyclotron effective mass (m*~ 0.05me), very high mobility of ~ 2.2  10 4 cm -2 /V-sand the signature of topological protected surface states in the compound. The MR data follows the three dimensional Weyl semimetal like behavior. Kohler’s rule is obeyed at low t...

The pressure-dependent behaviour of NaMn7O12 (up to 40 GPa) is studied and discussed by means of single-crystal X-ray diffraction and resistance measurements carried out on powdered samples. A transition from thermally activated transport mechanism to semimetal takes place above 18 GPa, accompanied by a change in the compressibility of the system. On the other hand, the crystallographic determi...